Pneumatic modulating relay



Sept 1953 H. L. BOWDITCH PNEUMATIC MODULATING RELAY I Filed March 14, 1951 INVENTOR. HOEL L. BOWDITOH Fr Q H II I 8 I 2 I 6 m l I F v v 9 m f M 2 7, w u a w l 3 3 3 4 5 4 a/ k m M a 2 3 5 v u 4 4 a a a 4 2 o 3 H mm m a 7 o 6 I w m 2 I- ill a M 2 O 2 J 6 I 4 8 2 l .liiilllillll I lllllflllo Q \\\\\\\\\\\5 FIG. 2

Patented Sept. 15, 1953 UNITED STATES PATENT OFFICE PNEUMATIC MODULATING RELAY Hoel L. Bowditch, Foxboro, Mass., assignor to The Foxboro Company, Foxboro, Mass., 2. corpcra tion of Massachusetts Application March 14, 1951, Serial No. 215,611

1 Claim. 1

This invention relates to instruments of the type used. for recording, indicating, and/or controlling values of variable conditions such as temperature, pressure, flow, and the like.

It is particularly concerned with a pneumatic action device for use in such instruments.

Such instruments use condition sensing elements responsive to value changes in the variable conditions, and the response of the sensing element to the condition change is transmitted to an action device in the instrument for operating a recording, indicating, or control unit.

It is an object of this invention to provide a new and improved device of this nature.

The device of this invention is inexpensive, compact, and accurately eifective with small forces, and is in the form of a balance arrangement which is productive of a pneumatic operating output force proportionally representative of the sensing element response to the variable condition change.

An illustrative embodiment of this invention is shown in the accompanying drawings, in which:

Figure I is a diagrammatic illustration of a nozzle and ball piston unit pneumatic device; and

Figure II shows the detail of the ball piston pneumatic unit.

The embodiment of this invention as shown in Figure I is an arrangement for controlling the temperature of a process.

As will be explained, temperature variations in the process are made to control an input to the process. This is done by translating movement produced by the response of a thermometer in the process into proportional pneumatic pressure for application to a valve in the input, and this translation is accomplished by a pneumatic action device, in this instance comprising a flapper unit, a nozzle, a ball piston pneumatic unit, and a pneumatic relay.

Referring to Figure I, at the lower left, a proc 'ess tank is indicated at [0. Projecting into the tank It is a thermometer I l for sensing temperature changes in the process. This thermometer may be of the common liquid filled type.

Connected to the thermometer II is a tube I2 through which the response to temperature varia tion is travelled to produce movement in a spiral Bourdon tube l3. Secured to the Bourdon tube to receive its movement, is a connector I4. This connector is secured to a lightweight flapper unit generally indicated at [5.

The portion of the flapper unit IE to which the connector I4 is secured is in the form of a T as at it, w t the per m ter 14 secured thereto at the base of the T. This T is mounted on a pivot l! at the point of intersection of the upright and cross portions of the T. Thus a temperature variation in the tank l0 results in a pivotal movement of the T It. This movement, or at least a part of it, depending upon the particular dimensions and configurations of the T [6 and. the remainder of the structure, is transferred to the remainder of the flapper unit through engagement with a pin it, extending through the cross portion of the T, generally parallel with the pivot I1. Several openings are located in the cross portion of the T, and the pin Hi may be placed in any one of them to vary the direction or degree of transfer of the motion of the T l 6 to the remainder of the flapper unit.

The remainder of the flapper unit comprises two members l9 and 2!] which are secured to each other to form a unitary structure. The member [9 is generally in the form of a W with its two outer legs and its base formed rigidly, and its center leg formed as a flat resilient member of substantially the same length as the outer legs. The member 20 is resilient and generally in the form of a triangle with a triangular central opening, a strip connection 2| extending from its base and an arm 22 on the strip connection, substantially parallel with the base of the triangle and with the cross portion of the previously mentioned T member it when the T is upright. The W member l9 and the triangle 2!! are rigidly secured together along their bases, with the apex of the triangle overlying the upper end of the middle leg of the W, but somewhat short of the extremity thereof. Through the apex of the resilient triangle member 20 there is mounted an adjustment screw 23 which engages the resilient center leg of the W member I9. Thus more or less pressure may be adjustably exerted on the center leg of the W.

The W member [9 is pivotally mounted about an axis 24 which extends through the outer ends of the outer legs of the W l9 through mounting bosses 25. This axis 24 is perpendicular to the axis of the pivot I! of the previously mentioned T member it, and is parallel to the arm 22 on the triangle member 20.

Connection between the T member I6 and the remainder of the flapper unit is accomplished through the engagement of the pin [8 in the T member with the arm 22 on the triangle member 26. Thus a temperature variation in the process tank It, within arranged limits results in a movement of the structure comprising the W member [9 and the triangle member 20, about the axis 24.

Associated with the flapper l5, and specifically with the resilient center leg of the W member l9, there is a pneumatic nozzle 26 and a pneumatic ball piston unit 27. This nozzle and piston are aimed at the center leg of the W member [9 in such a manner that pneumatic flow from the nozzle and force of the ball piston unit will be directed against the center leg of the W member, and movement of the flapper unit about the axis 24 releases or restricts pneumatic flow from the nozzle. The pneumatic flow from the nozzle 25 is minor so that the flow has no operative efiect on the position of the center leg of the W member. Force from the ball piston unit 2'! however, is used to move the center leg of the W member in opposition to its movement with respect to the nozzle 26 as obtained from a temperature variation in the process tankl 0.

The nozzle 26 and the ball piston unit 21 are both connected to a pneumatic relay, generally indicated at 28. The construction and operation of this type of pneumatic relay is shown and described in my pending patent application for a Controller, filed August 21, 1946, Serial No. 692,102, now Patent No. 2,631,570 of March 17, 1953. Generally speaking there is a pneumatic path through the relay through which a substantial pneumatic operating pressure may be travelled. This path is opened or closed, partially or fully, through movement of a diaphragm, with the diaphragm movement controlled by a minor, or throttling, pneumatic pressure.

.As shown in Figure I, the relay 28 is provided, at the top, with a pneumatic pressure input 29. The relay has a power chamber 30 and a secondary chamber 3!, with the input pressure having unrestricted access to the power chamber 30 and restricted access to the secondary chamber 3| through a restrictor passage 32. These chambers are separated by a diaphragm 33, and the power chamber 33 is divided into two subchamhers joined by a passage 34 axially perpendicularly ali ned with the central portion of the diaphragm 33. The diaphragm carries a valve unit 35 which extends through the passage 34, being engaged in the power chamber by a spring 35 as an aid in closing the valve.

From the passage 32 between the subchambers of the power chamber 30 and extending into neither, there is an output passage 31. Thus, with the valve 35 open, an unrestricted pneumatic path is provided through the relay by way of the input 23, one of the subchambers of power chamber 30, chamber passage 34, and the output passage 31. At the bottom of the relay there is a passage from the power subchamber adiacent the diaphragm, as at 38, operable as a bleed to atmosphere.

Referring again to the nozzle 26, it is a pneumatic bleed nozzle and is connected by a tube 39 to the relay secondary chamber 3 l. Thus a minor pneumatic flow is provided from the nozzle 25 by way of the relay input 29 and the restrictor opening 32. The ball piston pneumatic unit 2? is connected by a tube 49 to the relay output passage 3'! so as to be provided with a substantial pneumatic force when the relay valve 35 is open. Further, the relay output passage 3'! is connected, as shown at the bottom of the drawing, to a pneumatic valve 4! in a pipe line 42 leading into the process tank M. The temperature of the process in the tank I!) is controlled by a heating or cooling medium applied to the process through the pipe line with this application controlled by the valve Referring to Figure II, it is simply a showing of the detail of the ball piston unit 21. It comprises a cylinder with an open outer end and a ball 45 smoothly fitted therein for movement along the axis of the cylinder. Engagement of the ball with the flapper resilient leg We as shown in dotted lines at 46 keeps the ball from leaving the piston unit and is the manner of applying the force from the relay 28 to the flapper unit resilient leg lSa.

In the operation of the device, the flapper unit 15 is arranged to tend to fall by gravity, about the axis 24, and toward the bleed nozzle 26. To set up an example. assume the arrangement shown in Figure I, and assume that the temperature in the process tank I0 is such that the flapper unit is supported by the pin I8 and that the resilient leg [5a is spaced from the bleed nozzle 26. Under all conditions, the free end of the flapper leg ltd is resting on the ball piston unit 21.

Under he above conditions, assume, further, a drop in temperature. The resulting action is that the pin It is moved downward, and under the action of gravity, the flapper unit [5 follows the pin H3 down, by movement about the flapper unit axis 24. Through this movement, the flapper resilient leg l9aapproaches the bleed nozzle 28, gradually throttling off the pneumatic flow therefrom.

As this flow is restricted, pressure builds up in the relay 28 in the secondary chamber 3|, resulting in movement of the diaphragm 33 and in opening the valve formed by the passage 35 and the valve unit 35; A pneumatic pressure from the power chamber 30 is thus introduced into the relay output passage 3'! and into the ball piston unit M.

This pressure in the ball piston unit is applied upwardly against the free end of the flapper unit resilient leg [9a. This pressure, since it is applied, essentially, on the axis 24 of the flapper unit l5, has, for practical purposes, no effect on the movement of the flapper unit l5 about the axis 24. However, the ball piston pressure does act upon the resilient leg [9a and the resilient member 23. This action lifts the leg [9a from the bleed nozzle 25, or at least, resists the movement of the leg [9a toward the nozzle 26, that is, the downward movement caused by the downward pivoting of the flapper unit I 5 as a whole. Thus a balance may be achieved at any position of the pin 58, within a given range.

The action is reversed under rising temperature conditions. As the flapper unit I5 is lifted about its pivot 24, the resilient leg I90. is lifted away from the bleed nozzle 26. The consequent increase of pneumatic flow from the nozzle 25 results in reduced pressure in the ball piston unit 2'! and the resilient leg Ha through its resilience, tends to approach the nozzle 26, so a balance may again be achieved.

The force thus determined as that necessary from the ball piston unit to hold the flapper resilient leg in its position of balance, is the output force of the device, as applied through the relay output passage 31 to the pipe line valve 41. This output force is proportionally related to the Bourdon movement as produced by temperature changes in the process tank Ill.

The ball piston unit 2-! is so located in the par-- ticular structure shown as to provide intersection between the longitudinal axis of the unit 2'? and the flapper unit pivot axis 24. The flapper unit resilient member [9a may thus pivot on the ball of the ball piston unit as the flapper unit is pivoted about its axis 24, without varying the leverage factor on the flapper resilient member. Such a factor may be impressed on the resilient member as previously indicated herein, by adjustment of the screw 23.

The output force proportion referred to above is variable by changing the location of the nozzle 26 with respect to the flapper unit and with respect to the ball piston unit. In this instance the bleed nozzle tube 36 is flexible and the nozzle 26 may be adjusted toward or away from the ball piston unit 21. This adjustment is accomplished by movement of a sliding arm 43, as in Figure I, which is held in adjusted position by the binding action of pins 44. The pins hold the arm 43 firmly, and yet permit sliding adjustment of the arm. In this adjustment as the nozzle approaches alignment with the rigid bases of the flapper unit W member I 9 and triangle 20, the proportion relation is reduced and with the nozzle in direct alignment with the mentioned bases, the proportion becomes a one to one relation because the bending of the flapper resilient leg no longer changes the relation between the nozzle and the flapper unit. The device thus becomes a simple on-off action device operated simply by the movement of the flapper unit about the axis 24 in closing or opening the nozzle 26 and consequently operating the pipe line valve 41 only from full on to full off positions, or the reverse.

I claim:

In a pneumatic action device for use in instruments as described, a nozzle, means for producing a pneumatic flow through said nozzle, a flapper unit mounted in the path of said pneumatic flow for pivotal movement about an axis with respect to said nozzle so as to vary said flow, said flapper unit including a flexible portion movable independently of said unit movement as another means of varying said flow, means for producing said unit movement in response to changes in a variable condition, a pneumatic relay connected to said nozzle and operable by variations of said flow to produce a relay output force, and a bail piston pneumatic unit arranged to direct said relay output force against said flapper unit flexible portion through ball contact therewith substantially on said flapper unit axis to produce said independent movement in opposition to said unit movement, whereby pivoting of said flapper unit about said axis causes said flexible portion to pivot about said ball without further flexing, and said nozzle and said flapper unit achieve a particular position relation, with said relay output force available as a working force which is proportionally representative of said response to said variable condition change.

HOEL L. BOWDITCH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,035,966 Hubbard et a1. Mar. 31, 1936 2,236,097 Hubbard et a1 Mar. 25, 1941 2,250,341 Wunsch July 22, 1941 2,436,451 Rosenberger Feb, 24, 1948 2,536,198 Matner et a1. Jan. 2, 1951 2,547,224 MacGuire Apr. 3, 1951 2,585,347 Robins Feb. 12, 1952 

